1. Field of the Invention
The present invention relates to upgrading a spindle motor for an optical disk and more particularly to making a motor bearing high in service life and low in all of load, vibration and noise.
2. Description of the Prior Art
In reply to the recent demand for higher performance of various office automation devices, the operating speeds of those devices are becoming higher and higher. At the same time, spindle motors for driving disks in various devices are also required to rotate at higher speeds to meet the demand for speed-up. Once spindle motors become high in their rotational speeds, it is inevitably required for their bearing mechanisms that the loss of torque be low. As a result, ball bearings are used to meet this demand. However, this tendency leads to an increase of cost. In view of this point and in order to reduce the cost of bearings, there actually are employed plain bearings formed of a sintered alloy impregnated with a lubricating oil.
If ball bearings are used in a conventional high-speed rotation type spindle motor, it is possible to decrease the loss of torque and attain a high rotational accuracy, but there is the tendency that the higher the rotation, the more conspicuous the resulting vibration and noise. In the case of plain bearings, they are superior in point of reducing vibration and noise in comparison with ball bearings, but involve the problem that the loss of torque increases and that the rotational accuracy becomes unstable due to a clearance between the sintered alloy of the bearings and a rotary shaft of the motor.
The present invention has been accomplished in view of the above-mentioned problems and it is an object of the invention to provide a bearing structure in a brushless DC motor which bearing structure can diminish the loss of torque caused by rotational contact and can suppress vibration and noise.